The present invention relates to a brazeable aluminum material for use to construct a heat exchanger or any other apparatus or the like which are manufactured by the brazing technique, and also relates to a method of producing the brazeable aluminum material.
The term "aluminum" used herein is meant to include aluminum alloys.
Aluminum is used widely to manufacture various kinds of brazed articles and apparatuses, because it is comparatively light, highly processable and heat conductive.
An easily brazeable aluminum brazing sheet, which has widely been used for that purpose, is composed of an aluminum core sheet having a surface `roll-clad` with a layer of a brazing agent. For certain kinds of aluminum materials including those which are prepared by the extruding method, the cladding of said agent is impossible or very difficult.
The `thermal spraying` method is known and has been proposed to form a brazing agent layer on aluminum materials such as the extruded one which can hardly be clad with said layer (see for example the Japanese Patent Publication Sho. 63-1152, and Unexamined Publications Hei. 1-157794, ibid. Sho. 63-119974, ibid. Hei. 1-107961 and ibid. Hei. 2-46969)
However some aluminum materials coated with the thermally sprayed brazing agent are poor in brazeability. The present inventors have investigated those defective cases and found the following facts to be a cause thereof.
Generally, the prior art methods of thermal spraying do use as the brazing agent a wire of brazeable alloy, as disclosed in the Patent Publications Sho. 63-1152 or Hei. 1-157794. The wire of the brazing agent thus has to completely melt to form liquid particles sticking to an aluminum core sheet. A high temperature causing the agent to completely melt will produce on the core sheet a resistant oxide membrane, which renders less brazeable the aluminum material. The sprayed liquid particles solidify on the core sheet to form a continuous layer of the brazing agent. A fine internal texture found in such a layer however resembles that which would appear after the brazing of aluminum material. Thus, this layer can no longer act as any effective brazing agent layer in subsequent use. Further, in the case of the plasma-arc spraying at extremely high temperatures, a considerable amount of the brazing agent is likely to evaporate during or after melt deposition on the aluminum surface. Consequently, an undesirable change in the agent would impair its brazeability.
An object of the present invention is therefore to provide a brazeable aluminum material comprising an aluminum core which is coated with a thermally sprayed brazing agent layer but free from the problem of unsatisfactory brazeability inherent in the prior art thermally sprayed layer.
A further object of the present invention is to provide a method of producing such a brazeable aluminum material as just noted above.
A brazeable aluminum material which achieves the above comprises an aluminum core having its surface coated with a thermally sprayed brazing agent layer which substantially is composed of a number of unmolten granular particles of a brazing agent. In order to achieve the further object, the method provided herein to produce a brazeable aluminum material composed of an aluminum core comprises the steps of preparing a powder of a brazing agent and then thermally spraying the powder onto the aluminum core under a condition such that only surfaces of most of powder granules are molten, with an interior of each granule remaining unmolten.
Other objects, features and advantages of the present invention will become clear from the description made below referring to the drawings.